Wireless and power-source-free extravasation and infiltration detection sensor circuitry provided on a substrate with signal splitter

ABSTRACT

A system detects extravasation or infiltration by segregating active components that drive a passive sensor for economical single use. A receiving antenna of the passive sensor receives a transmitted signal comprising RF electromagnetic power. A first circuit transmits a first portion of the received signal through a body portion. A sensor detects a resultant signal from the body portion. A second circuit combines a reference signal comprising a second portion of the received signal with the resultant signal so as to define an output signal. A transmit antenna transmits the output signal to a receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/241,179 filed on Mar. 11, 2014, which is the National Stage ofInternational Application No. PCT/US2012/052801, filed Aug. 29, 2012,which claims the benefit of U.S. Provisional Application No. 61/530,436,filed Sep. 2, 2011, U.S. Provisional Application No. 61/530,454, filedSep. 2, 2011, and U.S. Provisional Application No. 61/530,441, filedSep. 2, 2011, the content of each of which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention relates generally to the detection of fluids intissue, and, more particularly, to apparatuses, systems and methods fordetection of changed, elevated or abnormal fluid levels in tissue.

BACKGROUND ART

Changed, elevated or abnormal fluid levels in living tissue can resultfrom a number of physiological conditions. For example, edema is anabnormal accumulation of watery fluid in the intercellular spaces ofconnective tissue. Edematous tissues are swollen and, when punctured,secrete a thin incoagulable fluid. Edema is most frequently a symptom ofdisease rather than a disease in itself, and it may have a number ofcauses, most of which can be traced back to gross variations in thephysiological mechanisms that normally maintain a constant water balancein the cells, tissues, and blood. Among the causes may be diseases ofthe kidneys, heart, veins, or lymphatic system; malnutrition; orallergic reactions.

Moreover, bleeding (hemorrhage) can cause blood to collect and clot(hematoma). Hematomas can, for example, occur beneath the outermost ofthree membranes that cover the brain (meninges) as a result of a headinjury. There are two types of cranial subdural hematomas. An acutesubdural hematoma occurs soon after a severe head injury. A chronicsubdural hematoma is a complication that may develop weeks after a headinjury. Such a head injury may have been so minor that the patient doesnot remember it. An epidural hematoma is a traumatic accumulation ofblood between the inner table of the skull and the stripped-off duralmembrane. The inciting event often is a focused blow to the head. It isoften difficult to detect hematomas, particularly when the hematomaoccurs well after the time of an injury.

In addition to accumulation of body fluids, elevated fluid levels intissue can arise as a result of introduction of a fluid into the body,for example, during an injection procedure. In that regard, in manymedical diagnostic and therapeutic procedures, a physician or otherperson injects fluid into a patient's blood vessels. Moreover, in recentyears, a number of injector-actuated syringes and powered injectors forpressurized injection of contrast medium in procedures such asangiography, computed tomography, ultrasound and NMR/MRI (NuclearMagnetic Resonance/Magnetic Resonance Imaging) have been developed.

Extravasation or infiltration is the accidental infusion or leakage ofan injection fluid such as a contrast medium or a therapeutic agent intotissue surrounding a blood vessel rather than into the blood vesselitself. Extravasation can be caused, for example, by rupture ordissection of fragile vasculature, valve disease, inappropriate needleplacement, or patient movement resulting in the infusing needle beingpulled from the intended vessel or causing the needle to be pushedthrough the wall of the vessel. High injection pressures and/or rates ofsome modem procedures can increase the risk of extravasation. Incomputed tomography, for example, contrast injection flow rates can bein the range of 0.1 to 10 ml/s.

Extravasation can cause serious injury to patients. In that regard,certain injection fluids such as contrast media or chemotherapy drugscan be toxic to tissue. It is, therefore, very important when performingfluid injections to detect extravasation as soon as possible anddiscontinue the injection upon detection.

In U.S. Pat. No. 7,122,012 to Bouton, et al., issued Oct. 17, 2006,which is hereby incorporated by reference in its entirety, a method wasdisclosed for detecting a change in the level of fluid in tissue in afirst area of a body. Steps included applying electromagnetic energy,preferably in the frequency range of approximately 300 MHz toapproximately 30 GHz, to a first volume of the body; measuring aresultant or returned signal; comparing the signal to a reference signalto determine if the fluid level in the tissue has changed. In oneembodiment, the method detected changes in the level of fluid in tissueof a body by applying electromagnetic energy to a first volume of thebody over a period of time; measuring a resultant signal or a signalreturned from the tissue; and comparing the signal to a reference signalto determine if a level of fluid in the tissue has changed during theperiod of time.

DISCLOSURE OF INVENTION

The following presents a summary in order to provide a basicunderstanding of some aspects of the disclosed aspects. This summary isnot an extensive overview and is intended to neither identify key orcritical elements nor delineate the scope of such aspects. Its purposeis to present some concepts of the described features in a form as aprelude to the more detailed description that is presented later.

In accordance with one or more aspects and embodiments, and thecorresponding disclosures thereof, various features of the invention aredescribed in connection with a wireless and passive sensor (no localpower source is required on the sensor) of a system for detectingextravasation or infiltration. By segregating active components thatdrive the passive sensor via Radio Frequency (RF) transmission, thepassive sensor can be economically disposed of after use. Thereby,health protocols in an institutional setting can be enhanced. Moreover,the passive sensor allows a degree of mobility for a wearer by beinglinked via the RF transmission.

In a first aspect, the present invention provides a passive sensor thatcomprises a receiving antenna for receiving a transmitted signalcomprising RF electromagnetic power as a received signal. A firstcircuit transmits a first portion of the received signal through a bodyportion. A sensor detects a resultant signal from the body portion. Asecond portion of the received signal defining a reference signal passesthrough a reference pathway that is not affected by fluid or otherchanges in the tissue. The combination of the signal that has passedthrough the body portion, i.e., the resultant signal and the referencesignal defines an output signal. A transmit antenna transmits the outputsignal to a receiver for use in determining a change in a level of fluidin the body portion.

In a second aspect, the present invention provides a system fordetecting extravasation that comprises a sensor according to the firstaspect of the invention. In some embodiments, the system of theinvention may comprise a signal generator for transmitting a transmittedsignal comprising RF electromagnetic power selected for beingtransmittable through a body portion in relation to an amount of fluidin the body portion due to extravasation. A passive sensor comprises areceiving antenna for receiving the transmitted signal as a receivedsignal, a first circuit for transmitting a first portion of the receivedsignal through the body portion, a sensor for detecting a resultantsignal from the body portion, a second circuit for combining a referencesignal comprising a second portion of the received signal with theresultant signal so as to define an output signal, and a transmitantenna for transmitting the output signal. A signal processor may thenreceive the transmitted output signal for use in determining a change influid level in the body portion.

In some embodiments, the signal processor further performs a ratiocomparison of peak amplitude of the resultant signal and the referencesignal of the transmitted output signal.

In other embodiments, the signal generator may use a series of timedomain pulses of electromagnetic power. The passive sensor may furthercomprise a first delay circuit for delaying a selected one of the firstportion of the received signal comprising the time domain pulse and thesecond portion of the received signal comprising the time domain pulseas the reference signal. In a particularly suitable embodiment, a seconddelay circuit delays the other one of the first portion and the secondportion of the time domain pulse. The first and second delay circuitsmay be configured to separate in time the resultant signal and thereference signal from each other as well as a noise pulse at the sensorarising due to a reflected portion of the transmitted signal.

In further embodiments, the receiving antenna further receives thetransmitted signal predominantly in a range of greater than 1.5 GHz toapproximately 30 GHz over a period of time. In a particular aspect, therange is less than 10 GHz.

In some embodiments, the transmitted signal may comprise a sweep ofcontinuous wave electromagnetic power across a frequency range.

In further embodiments, a substrate is provided to support one or more,and suitable each of the receiving antenna, the first circuit fortransmitting, the second circuit for combining, the sensor, and thetransmit antenna.

In a third aspect, the present disclosure provides a method fordetecting extravasation. A transmitted signal is transmitted comprisingRF electromagnetic power selected for being transmittable through a bodyportion in relation to an amount of fluid in the body portion due toextravasation. The transmitted signal is received as a received signal.A first portion of the received signal is transmitted through the bodyportion. A resultant signal is detected from the body portion. Areference signal comprising a second portion of the received signal iscombined with the resultant signal so as to define an output signal. Theoutput signal is transmitted. The transmitted output signal is received.The output signal is used to determine a change in fluid level in thebody portion. In a particularly suitable embodiment of this aspect, themethod may be performed using a device, apparatus/system according tothe invention.

In some embodiments, a ratio comparison of peak amplitude of theresultant signal and the reference signal is performed.

In another embodiment, the transmitted signal may further comprise atime domain pulse of electromagnetic power. The method may furthercomprise delaying a selected one of the first portion of the receivedsignal comprising the time domain pulse and a second portion of thereceived signal comprising the time domain pulse as the referencesignal. The reference signal is combined with the resultant signal aspulses separated as a function of time. In a particularly suitableembodiment, the other one of the first portion and the second portion ofthe time domain pulse is delayed to separate in time the resultantsignal and the reference signal from each other as well as blanking anoise pulse arising due to a reflected portion of the transmitted signalfrom an ambient environment.

In an additional embodiment, the transmitted signal may be transmittedin a range of greater than 1.5 GHz to approximately 30 GHz over a periodof time. In a particularly suitable embodiment, the range is less than10 GHz.

To the accomplishment of the foregoing and related ends, one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative aspectsand are indicative of but a few of the various ways in which theprinciples of the aspects may be employed. Other advantages and novelfeatures will become apparent from the following detailed descriptionwhen considered in conjunction with the drawings and the disclosedaspects are intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed aspects will hereinafter be described in conjunction withthe appended drawings, provided to illustrate and not to limit thedisclosed aspects, wherein like designations denote like elements, andin which:

FIG. 1 is a schematic block diagram of a system for detecting a changein a fluid level in tissue using an RF driven passive sensor, accordingto one aspect;

FIG. 2 is a schematic block diagram of a system for detecting a changein a fluid level using a time-domain RF pulse with combined andtransmitted time-delayed reference and resultant signals for remotesignal processing, according to one aspect; and

FIG. 3 is a flow diagram of a methodology for detecting a change in thefluid level of tissue, according to one aspect.

MODES FOR CARRYING OUT THE INVENTION

While the sensors, systems and methods of the present invention aregenerally applicable to the sensing of a wide range of fluids within avariety of body tissues (whether a body fluid or an introduced fluid),the present invention is primarily described herein with reference tothe representative example of extravasation of a fluid intended to beinjected into a vascular structure. However, one skilled in the art withthe benefit of the present disclosure can appreciate that elevated,abnormal or changing levels of generally any fluid can be detected usingthe sensors, systems and methods of the present invention. Detection ofbody fluids in the present invention includes, but is not limited to,the detection of fluid changes as a result of edema, hematoma, rupturedbowel and colostomy tubing leakage into the peritoneal cavity.Introduced or foreign fluid detectable in the present invention includefluid introduced via generally any technique known in the medical artsincluding, but not limited to, injection, infusion and IV drip. Changesin complex permittivity and permeability as a result of changing fluidlevels in tissue are detected by application of electromagnetic power tothe tissue and detection of a resultant signal.

Complex permittivity and permeability govern how an electromagnetic wavewill propagate through a substance. Complex permittivity typically hasthe greatest effect since it varies significantly between tissue typesand fluids of interest. The complex permeability of various tissues andmany fluids of interest is approximately that of a vacuum, reducing theeffect of this parameter. However, some fluids such as MRI contrastagents may have an appreciable complex permeability difference fromtissue. Although blood contains small amounts of iron, the permeabilityvalue for any significant volume of blood is typically insignificant.Complex permittivity is generally expressed asε*=ε′−jε″

wherein ε′ is the real component of the complex value and is known asthe dielectric constant or sometimes simply referred to as the“permittivity.” The term ε″ is the imaginary component of the complexvalue and is often referred to as the “loss factor.” The ratio of ε″/ε′is known as the “loss tangent.” The complex permittivity (and sometimespermeability) of certain substances differ from the body tissue atcertain frequencies. In the present invention, such differences inpermittivity and/or permeability are used for the detection and levelmonitoring of certain fluids and substances in biological tissue.

The studies of the present innovation have shown that electromagneticpower having, for example, a frequency in the range of approximately 300MHz to approximately 30 GHz (and, more preferably, in the range ofapproximately 1 GHz to approximately 10 GHz, and, even more preferably,in the range of approximately 3 GHz to approximately 5 GHz to 10 GHz)provides good penetration into tissue. In general, such electromagneticpower is launched into the subcutaneous tissue and a resultant signal ismeasured. Electromagnetic power in the frequency range set forth abovehas been found to transmit through the skin and to transmit or propagatewell within, for example, fat. Good transmission through the fat layeris beneficial for detection of extravasation as many extravasationsoccur in the fat layer. The sensitivity to extravasation of the systems,devices and methods of the present invention is thus increased ascompared, for example, to impedance plethysmography. In the case ofimpedance plethysmography, the majority of the electrical current passesthrough highly conductive layers such as skin and muscle in whichextravasation is much less likely to occur.

While using RF electromagnetic power to detect extravasation andinfiltration has thus been established as an effective approach, thepresent innovation addresses certain clinical aspects. Fluid injections,liquid infusions, and IV drips require that measures be taken to avoidinfection. In particular, tubing and dressings are typically disposableand frequently replaced. Sensing extravasation or infiltration canentail placement of transmitters and receivers close to an insertionpoint on the skin of a patient. As such, a device for detectingextravasation or infiltration of fluids in the tissue can pose as asource of infection or contamination if not similarly disposable.However, circuitry for generating and analyzing RF electromagneticsignals typically entails use of digital signal processing equipmentthat can prove to be too expensive for single uses.

Thus, a passive sensor of a system is driven by transmitted RFelectromagnetic power, passes the power through tissue of a body portionfor detecting a level of fluid, and transmits back an output signal forremote digital signal processing. Thereby, a relatively inexpensivecomponent implementation can be incorporated into the passive sensor. Incertain clinical environments, more than one passive sensor can bedriven by the transmitted RF electromagnetic power since thetransmission in response can be delayed in time as well as being at areduced power level.

Various aspects are now described with reference to the drawings. In thefollowing description, for purposes of explanation, numerous specificdetails are set forth in order to provide a thorough understanding ofone or more aspects. It may be evident, however, that such aspect(s) maybe practiced without these specific details.

In FIG. 1 , the present disclosure provides a system 100 for detectingextravasation or infiltration. A signal generator 102 transmits atransmitted signal 104 comprising Radio Frequency (RF) electromagneticpower selected for being transmittable as depicted at 106 or 106′through a body portion 108 in relation to an amount of fluid 110 in thebody portion 108 due to extravasation or infiltration.

A passive sensor 112 has a receiving antenna 114 for receiving thetransmitted signal 104 as a received signal 116. The transmitted signalis split via a conventional splitter (not shown) into first and secondportions. A first circuit 118 transmits the first portion of thereceived signal 116 through the body portion 108. A sensor 120 detects aresultant signal 122 from the body portion 108. The second portion ofthe received signal 116 travels through a reference pathway such as adelay line, wherein the second portion of the received signal is notaffected by fluid or other changes in the tissue. A second circuit 124combines the reference signal 126 comprising the second portion of thereceived signal 116 with the resultant signal 122 so as to define anoutput signal 128. A transmit antenna 130 transmits the output signal128 as a transmitted output signal 132.

A signal processor 134 receives the transmitted output signal 132 as areceived signal and uses the output signal 132 to determine a change inthe fluid level within the body portion 108. In the illustratedembodiment, the signal processor compares a ratio of a peak amplitude ofthe resultant signal 122 to a peak amplitude of the reference signal126, which ratio is determined from the output signal 132 during fluidinjection into a patient body portion 108, with a ratio of a peakamplitude of a resultant signal to a peak amplitude of a referencesignal taken earlier in time via the passive sensor 112 during abaseline detection operation, e.g., just before fluid is injected intothe body portion 108. In FIG. 1 , a first portion 106 of the receivedsignal 104 corresponds to a signal being transmitted through the bodyportion 108 during a baseline operation and a first portion 106′ of thereceived signal 104 corresponds to a signal being transmitted throughthe body portion 108 later in time when fluid has accumulated in thebody portion 108 such that the first portion 106′ passes through theaccumulated fluid in the body portion 108.

In another aspect, the transmitted signal 104 further comprises a timedomain pulse of electromagnetic power. The passive sensor 112 furthercomprises a first delay circuit 136 for delaying a selected one of thefirst portion of the received signal 116 comprising the time domainpulse and the second portion of the received signal comprising the timedomain pulse as the reference signal 126. The second circuit 124 furthercombines the reference signal 126 with the resultant signal 122comprising pulses separated as a function of time by the first delaycircuit 136. In a particular aspect, a second delay circuit 138 delaysthe other one of the first portion and the second portion of the timedomain pulse. The first and second delay circuits 136, 138 areconfigured to separate in time the resultant signal 122 and thereference signal 126 from each other as well as a noise pulse at thesensor 120 arising due to a reflected portion of the transmitted signal104. Hence, there are two time delays for the first and second portionsof the received signal 104. First, the two time delays are intentionallylonger than room reflection delays so that the resultant signal 122 andthe reference signal 126 can be separated from the room reflections in afinal processing step. Second, the delay along the tissue pathway isintentionally different than the delay along the reference pathway, sothat the resultant signal 122 and the reference signal 126 can beseparated and analyzed. The delay along the reference pathway may belonger or shorter than the delay along the tissue pathway.

In another aspect, the receiving antenna 114 is further for receivingthe transmitted signal 104 in a range of greater than 1.5 GHz toapproximately 30 GHz over a period of time, and more particular therange is less than 10 GHz.

In an additional aspect, the passive sensor 112 includes a substrate 140for supporting at least the receiving antenna 114, the first circuit 118for transmitting, the second circuit 124 for combining, the sensor 120,and the transmit antenna 130.

In an exemplary aspect in FIG. 2 , a system 200 has a signal generator202, depicted as a time-domain pulse generator, that transmits atransmitted signal 204 as a time domain pulse via a transmit antenna(s)205 to cause transmission as depicted at 206 or 206′ through a bodyportion 208 in relation to an amount of fluid 210 in the body portion208 due to extravasation or infiltration.

To that end, a passive sensor 212 has a receiving (RX) antenna(s) 214for receiving the transmitted signal 204 (time domain pulse) as areceived pulse or received signal 216. Thus, the passive sensor 212comprises the RX antenna(s) 214 that receives a time domain impulsestream from a base unit 244 that includes the signal generator 202. Thisbase unit 244 uses time domain or ultra-wideband radar methods togenerate a series of impulses to be sent to the passive sensor 212. Thepassive sensor 212 then comprises a splitter 246 that splits first andsecond portions of the received signal 216 from the RX antenna(s) 214,respectfully, to a pathway 248 that will include the tissue of interestfor sensing fluid 210 and a pathway 250 that returns the second portionof the signal back to the base unit 244.

A first circuit 218 comprising a transmit antenna(s) transmits the firstportion of the received signal 216 through the body portion 208. Asensor 220 comprising a receiving antenna(s) detects a resultant signal222 from the body portion 208. A second circuit 224 combines the secondportion of the received signal 216, which second portion defines areference signal 226, with the resultant signal 222 so as to define anoutput signal 228. A transmit antenna(s) 230 transmits the output signal228 as a transmitted output signal 232.

A signal processor 234 serves as an extravasation/infiltration detectorby receiving the transmitted output signal 232 at a receiving antenna(s)235 as a received signal and for comparing a patient fluid injectionratio of the resultant signal 222 to the reference signal 226 takenduring patient fluid injection to a baseline ratio of a resultant signalto a reference signal generated earlier in time during a baselinedetection operation so as to detect a change from the baseline ratio,which change corresponds to a change in the fluid level in the bodyportion 208. If the patient fluid injection ratio is less than apredefined percentage of the baseline ratio, e.g., 90% of the baselineratio, then this can warrant an alert indicating that an unacceptablefluid level change has occurred. In FIG. 2 , a first portion 206 of areceived signal corresponds to a signal being transmitted through thebody portion 208 during the baseline operation and a first portion 206′of a received signal 204 corresponds to a signal being transmittedthrough the body portion 208 later in time when fluid 210 hasaccumulated in the body portion 208 such that the first portion 206′passes through the accumulated fluid 210 in the body portion 208.

In the exemplary implementation, the passive sensor 212 furthercomprises a first delay circuit 236 depicted as a delay line T1, fordelaying the first portion of the received signal 216 by a time “T1”prior to transmission through the body portion 208 so as to ensure thatthe first portion lags the second portion of the received signal 216. Ina particular aspect, a second delay circuit 238 delays the referencesignal 226 such that the reference signal 226 is separated in time,i.e., follows a noise pulse 239 at the sensor 220 arising due to areflected portion 241 of the transmitted signal 204 from an ambientenvironment 243, see FIG. 2 . In the illustrated embodiment, timeT1+T_(T) (signal delay in a patient body portion) is greater than timeT2. However, it is contemplated that time T2 may be greater thanT1+T_(T).

Hence, both pathways 248, 250 illustrated in FIG. 2 have first andsecond delay circuits 236, 238 (delay line T1 and delay line T2). Thedelay line T1 (first delay circuit 236) is present so that the signalthat propagates through the tissue will lag behind the T2 pathwaysignal. Delay line T2 (second delay circuit 238) allows room reflectionsto complete before the transmitted reference signal 226 is returned tothe signal processor 234 of the base unit 244. Thus, the shorter pathwayprovides the reference signal 226 that is independent of thetissue/fluid effects, but will include effects of distance changesbetween the passive sensor 212 and the base unit 244. Thereby, thesystem 200 looks for relative changes between the ratio of the currentresultant signal 222 to the current reference signal 226 to a baselineratio of a resultant signal 222A to a reference signal 226A generatedearlier in time during a baseline detection operation so as to detect achange from the baseline ratio, which change corresponds to a change inthe fluid level in the body portion 208. If the sensor 212 moves awayfrom the base unit 244, both the current resultant signal 222 and thecurrent reference signal 226 will decrease by the same percentage suchthat the ratio remains constant. If a fluid accumulation occurs withinthe body portion 208, the ratio of the current resultant signal 222 tothe current reference signal 226 will change relative to the baselineratio.

In use, a fluid supply 252 (e.g., infuser supply, contrast agentinjector, IV drip, etc.) provides fluid 254 via a conduit 256 (e.g.,catheter, needle, etc.) to a vascular body 258 of the body portion 208.As depicted at 210, extravasation or infiltration can cause an increasein a level of fluid that directly affects a signal 206′ propagatingthrough the tissue, such as based in a change in permittivity. Forexample, if the current reference signal 226 during patient fluidinjection equals the baseline reference signal 226A and an increase influid level has occurred in the patient, then the current resultantsignal 222 during patient fluid injection will typically be less thanthe baseline resultant signal 222A, see FIG. 2 . A resulting change indimensions of the body portion 208, as depicted at 260, can cause achange in the signal 206′.

In FIG. 3 , a method 300 for detecting extravasation or infiltration isdepicted. A transmitted signal is transmitted comprising RFelectromagnetic power selected for being transmittable through a bodyportion in relation to an amount of fluid in the body portion due toextravasation or infiltration (block 302). The transmitted signal isreceived as a received signal (block 304). A first portion of thereceived signal is transmitted through the body portion (block 306). Aresultant signal is detected from the body portion (block 308). Areference signal comprising a second portion of the received signal iscombined with the resultant signal so as to define an output signal(block 310). The output signal is transmitted (block 312). Thetransmitted output signal is received (block 314). A ratio of thecurrent resultant signal to the current reference signal is compared toa baseline ratio to detect a change in the fluid level in the bodyportion (block 316).

In another exemplary aspect, the transmitted signal further comprises atime domain pulse of electromagnetic power. The method further comprisesdelaying a selected one of the first portion of the received signalcomprising the time domain pulse and a second portion of the receivedsignal comprising the time domain pulse as the reference signal. Thereference signal is combined with the resultant signal as pulsesseparated as a function of time. In a particular aspect, the other oneof the first portion and the second portion of the time domain pulse isdelayed to separate in time the resultant signal and the referencesignal from each other as well as blanking a noise pulse arising due toa reflected portion of the transmitted signal from an ambientenvironment.

In an additional exemplary aspect, the transmitted signal is transmittedin a range of greater than 1.5 GHz to approximately 30 GHz over a periodof time. In a particular aspect, the range is less than 10 GHz.

In a further exemplary aspect, a user indication is presented of aselected one of an inoperative state, a nominal state and anextravasation state based upon the comparison.

In an alternative embodiment, the signal generator is a continuous wave(CW) source, which generates and transmits continuous wave power sweptacross a frequency range such as 2 GHz to 5 GHz (remaining at eachfrequency long enough for an amplitude and phase measurement by thereceiving circuitry to be made, which is typically a fraction of asecond). In the continuous wave embodiment, the passive sensor isgenerally the same as the passive sensor in the pulse source embodiment,discussed above. Hence, the passive sensor comprises a splitter forsplitting continuous wave power into first and second portions, firstand second delays for delaying (i.e., introducing differing phaseshifts) the first and second portions different amounts, a first circuitcomprising transmit and receive antennas and a second circuit forcombining a resultant signal, which is defined by the second portion ofthe continuous wave power after passing through tissue, and a referencesignal, which is defined by the first portion of the continuous wavepower. Amplitude and phase data for a plurality of frequencies, e.g.,256 frequencies, of the combined signal are provided to a signalprocessor, which converts the frequency domain information from thecombined signal into the time domain using inverse-Fourier or othertransforms known in the art. Once in the time domain, the processordetermines a first ratio of a peak amplitude of the resultant signal toa peak amplitude of the reference signal, which ratio is determined fromthe combined signal output during fluid injection into a patient bodyportion. The processor also determines a second ratio of a peakamplitude of a resultant signal to a peak amplitude of a referencesignal taken earlier in time during a baseline detection operation,e.g., just before fluid is injected into the body portion. The processorthen compares the first and second ratios to one another to detect achange in a fluid level in a body portion.

While the foregoing disclosure discusses illustrative aspects and/orembodiments, it should be noted that various changes and modificationscould be made herein without departing from the scope of the describedaspects and/or embodiments as defined by the appended claims.Furthermore, although elements of the described aspects and/orembodiments may be described or claimed in the singular, the plural iscontemplated unless limitation to the singular is explicitly stated.Additionally, all or a portion of any aspect and/or embodiment may beutilized with all or a portion of any other aspect and/or embodiment,unless stated otherwise.

It should be appreciated that any patent, publication, or otherdisclosure material, in whole or in part, that is said to beincorporated by reference herein is incorporated herein only to theextent that the incorporated material does not conflict with existingdefinitions, statements, or other disclosure material set forth in thisdisclosure. As such, and to the extent necessary, the disclosure asexplicitly set forth herein supersedes any conflicting materialincorporated herein by reference. Any material, or portion thereof, thatis said to be incorporated by reference herein, but which conflicts withexisting definitions, statements, or other disclosure material set forthherein, will only be incorporated to the extent that no conflict arisesbetween that incorporated material and the existing disclosure material.

What is claimed is:
 1. A passive circuit for sensing extravasation orinfiltration, comprising: a receiving antenna configured to receive atime domain pulse of electromagnetic power from a signal generator as areceived signal; a signal splitter configured to split the receivedsignal into a first portion and a second portion; wherein the firstportion and second portion of the received signal each represent thereceived signal; wherein the first portion of the received signal to betransmitted to tissue of a body portion of extravasation orinfiltration; and wherein the second portion of the received signaldefining a reference signal; a first delay circuit configured to delaythe first portion of the received signal to generate a delayed firstportion of the received signal; a first circuit configured to transmitthe delayed first portion of the received signal through the tissue ofthe body portion; wherein the first portion of the received signalincluding a first signal to be wherein the first portion of the receivedsignal including a first signal to be transmitted to tissue the a bodyportion at a first time and a second signal to be transmitted to tissueof a body portion at a second time, and wherein the first timerepresents a baseline before fluid has accumulated in the tissue of thebody and the second time is later than the first time; a sensorconfigured to detect a resultant signal from the body portion; theresultant signal representing changes in the first signal and secondsignal of the first portion of the received signal transmitted by thefirst circuit; a second delay circuit configured to delay the secondportion of the received signal to generate a second a delayed secondportion of the received signal, wherein the first and second delaycircuits are configured to separate in time the resultant signal, thereference signal, and a noise pulse at the sensor arising due to areflected portion of the transmitted signal; a second circuit configuredto combine the reference signal with the resultant signal to define anoutput signal, wherein the reference signal being unaffected by changesin the first and second signals of the first portion of the receivedsignal; and a transmit antenna configured to transmit the output signalto a base unit including the signal generator.
 2. The passive sensor ofclaim 1, wherein the transmitted signal comprises a sweep of continuouswave electromagnetic power across a frequency range.